Re: [PATCH V3] libxfs: use FALLOC_FL_ZERO_RANGE in libxfs_device_zero

["Darrick J. Wong" <darrick.wong@oracle.com>]

On Fri, Feb 21, 2020 at 09:22:12PM -0600, Eric Sandeen wrote:
> I had a request from someone who cared about mkfs speed(!)
> over a slower network block device to look into using faster
> zeroing methods, particularly for the log, during mkfs.
> 
> Using FALLOC_FL_ZERO_RANGE is faster in this case than writing
> a bunch of zeros across a wire.
> 
> Signed-off-by: Eric Sandeen <sandeen@redhat.com>
> ---
> 
> V2: Clean up all the nasty stuff I'd flung out there as a wild first
> cut, thanks Dave.
> 
> V3: make len_bytes a size_t; leave "end_offset" where it is for the loop
> use.  It's a bit odd but ... just don't mess with it for now, one patch
> one change.
> 
> diff --git a/include/builddefs.in b/include/builddefs.in
> index 4700b527..1dd27f76 100644
> --- a/include/builddefs.in
> +++ b/include/builddefs.in
> @@ -144,6 +144,9 @@ endif
>  ifeq ($(HAVE_GETFSMAP),yes)
>  PCFLAGS+= -DHAVE_GETFSMAP
>  endif
> +ifeq ($(HAVE_FALLOCATE),yes)
> +PCFLAGS += -DHAVE_FALLOCATE
> +endif
>  
>  LIBICU_LIBS = @libicu_LIBS@
>  LIBICU_CFLAGS = @libicu_CFLAGS@
> diff --git a/include/linux.h b/include/linux.h
> index 8f3c32b0..8d5c4584 100644
> --- a/include/linux.h
> +++ b/include/linux.h
> @@ -20,6 +20,10 @@
>  #include <stdio.h>
>  #include <asm/types.h>
>  #include <mntent.h>
> +#include <fcntl.h>
> +#if defined(HAVE_FALLOCATE)
> +#include <linux/falloc.h>
> +#endif
>  #ifdef OVERRIDE_SYSTEM_FSXATTR
>  # define fsxattr sys_fsxattr
>  #endif
> @@ -164,6 +168,24 @@ static inline void platform_mntent_close(struct mntent_cursor * cursor)
>  	endmntent(cursor->mtabp);
>  }
>  
> +#if defined(FALLOC_FL_ZERO_RANGE)
> +static inline int
> +platform_zero_range(
> +	int		fd,
> +	xfs_off_t	start,
> +	size_t		len)

Seems fine to me, though it's unfortunate to cap this at u32.

> +{
> +	int ret;
> +
> +	ret = fallocate(fd, FALLOC_FL_ZERO_RANGE, start, len);
> +	if (!ret)
> +		return 0;
> +	return -errno;
> +}
> +#else
> +#define platform_zero_range(fd, s, l)	(-EOPNOTSUP)

EOPNOTSUPP (two P's)

--D

> +#endif
> +
>  /*
>   * Check whether we have to define FS_IOC_FS[GS]ETXATTR ourselves. These
>   * are a copy of the definitions moved to linux/uapi/fs.h in the 4.5 kernel,
> diff --git a/libxfs/rdwr.c b/libxfs/rdwr.c
> index 0d9d7202..e2d9d790 100644
> --- a/libxfs/rdwr.c
> +++ b/libxfs/rdwr.c
> @@ -61,8 +61,18 @@ libxfs_device_zero(struct xfs_buftarg *btp, xfs_daddr_t start, uint len)
>  {
>  	xfs_off_t	start_offset, end_offset, offset;
>  	ssize_t		zsize, bytes;
> +	size_t		len_bytes;
>  	char		*z;
> -	int		fd;
> +	int		error, fd;
> +
> +	fd = libxfs_device_to_fd(btp->dev);
> +	start_offset = LIBXFS_BBTOOFF64(start);
> +
> +	/* try to use special zeroing methods, fall back to writes if needed */
> +	len_bytes = LIBXFS_BBTOOFF64(len);
> +	error = platform_zero_range(fd, start_offset, len_bytes);
> +	if (!error)
> +		return 0;
>  
>  	zsize = min(BDSTRAT_SIZE, BBTOB(len));
>  	if ((z = memalign(libxfs_device_alignment(), zsize)) == NULL) {
> @@ -73,9 +83,6 @@ libxfs_device_zero(struct xfs_buftarg *btp, xfs_daddr_t start, uint len)
>  	}
>  	memset(z, 0, zsize);
>  
> -	fd = libxfs_device_to_fd(btp->dev);
> -	start_offset = LIBXFS_BBTOOFF64(start);
> -
>  	if ((lseek(fd, start_offset, SEEK_SET)) < 0) {
>  		fprintf(stderr, _("%s: %s seek to offset %llu failed: %s\n"),
>  			progname, __FUNCTION__,
> 
>